Can't help you on the sealant. I've never found it necessary on any of my previous airplanes.

The most surefire way to avoid cracking involves a couple of steps during construction. First, always use a drill bit for plexiglass and go slow. Second, countersink with sufficient depth to ensure the skin will fully nestle down in the countersink without touching the plexi. Then third, overdrill the hole size to allow for a short piece of rubber tubing to fit over the screw shaft as it passes through the plexi. This seems to work for me and all my previous projects.

Randy,
I'm at the point of permanently mounting my rear window. Are you going to use your idea (above) of the rubber tubing through the holes?
Helped some friends strip down their -12 last night for annual, and they are seeing some crazing, eminating outward from some of the rear holes. I'm liking your tubing idea.
Are you still going to use the tubing on your aircraft?
Thank you-

Randy,
I'm at the point of permanently mounting my rear window. Are you going to use your idea (above) of the rubber tubing through the holes?
Helped some friends strip down their -12 last night for annual, and they are seeing some crazing, eminating outward from some of the rear holes. I'm liking your tubing idea.
Are you still going to use the tubing on your aircraft?
Thank you-

Quote:

Originally Posted by f1rocket

Can't help you on the sealant. I've never found it necessary on any of my previous airplanes.

The most surefire way to avoid cracking involves a couple of steps during construction. First, always use a drill bit for plexiglass and go slow. Second, countersink with sufficient depth to ensure the skin will fully nestle down in the countersink without touching the plexi. Then third, overdrill the hole size to allow for a short piece of rubber tubing to fit over the screw shaft as it passes through the plexi. This seems to work for me and all my previous projects.

****Edit: the crazing I mentioned above, small 'spider cracks' around the screw hole(s) was WAY over on the pilot side. Far beyond the reach of any fuel possibly ever reaching it!
Thank you-

Yes I am. You and I are neck and neck in the building. We seem to hit the same steps at the same time. I just finished up painting the interior this weekend and plan to install the window early next week.

I will buy some flexible rubber tubing that fits the screw shank and then drill up the window to the OD of the tubing. I'll cut little inserts the thickness of the plexi and use them as bushings.

Yes I am. You and I are neck and neck in the building. We seem to hit the same steps at the same time. I just finished up painting the interior this weekend and plan to install the window early next week.

I will buy some flexible rubber tubing that fits the screw shank and then drill up the window to the OD of the tubing. I'll cut little inserts the thickness of the plexi and use them as bushings.

Excellent, Randy. Thanks! I believe I'll follow suit and do the same. Like you mentioned earlier, if it has worked well for you in the past on many-many builds, it's sure worth trying again on these -12's.
I appreciate the tips!

Seems to be a common problem. I have a Goat-throat pump for 3 x 25 litre (6.6 gal) Scepter Containers on order for that very reason - to avoid spills.
I have also thought that maybe a 10mm wide 1.5mm thick (or less) adhesive (on one side) closed cell foam tape stuck to the fuse around the window would provide some elasticity, a weather seal and remove the need for tight screws.
Anyone out there ready to shoot me down for these ideas - fire away please.
John
Oz.

I installed my rear window yesterday and I enlarged the mounting holes and used rubber spacers as described in my previous post. I found some Bing fuel line that fit the #6 screw shanks perfectly and the OD was 1/4", which matched a plexi drill bit I had. After mounting the window, I can see why there are cracks and crazing around the screw holes. The window is a perfect fit but getting it installed all the way tends to put some stress on the screws and the holes.

I mounting all the screws loosely at first until I got them all started in the inserts. Then I pushed the window around to get all the bushings seated and aligned, then tightened down the screws. Worked perfectly.

I still need to go back and loosen up one side at a time and apply the fuel tank sealant. I'll do that once I get the canopy fitted.

According to manufacturer, gasoline will dissolve the polymers in Lexel. Not a wise choice for the 12

While searching for a sealant to install my Makrolon rear window in my RV-12, I was looking for good sealant and came across this thread. Considering that Lexel is recommended for sealing both acrylic and polycarbonate, I was interested until I saw this posting. So, I read the SDS, the tech data, the brochure and found nothing from the manufacturer that states this. I also noted that the product is 15-40% naphtha (petroleum) and toluene.

I then contacted Sascho, who makes Lexel Clear, and they said that while they would not recommend it for sealing a fuel tank, as extended contact will soften the polymer strings, however incidental contact by fuel (such as splashed fuel) should not be a problem.

The advantage of this product over Fuel Tank Sealant is that it’s much easier to remove should the day arise the window needs replacing.

I used Lexel Clear to seal my rear window and was easy to use and looks great.

I donít know what you guys are planning to do with the sealant, but consider what a problem it might be if you ever have to replace the rear window. I didnít put any sealant on the contact urface between plex and aluminum. Instead I masked a line 1/8Ē from the aluminum edge and applied clear RTV. I pulled the tape up before the RTV set and got a great inconspicuous seal at the edge. When I replaced my flat lexan window with the new molded one it came out with no problems. I sealed the new one with the same method.

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